Film scanning device



Oct. 23, 1945. J. KUFFER FILM SCANNING DEVICE Filed June 20, 1939 7/7van/or g W Patented Oct. 23, 1945 FILM SCANNING DEVICE Johannes Kiifler,Berlin, Germany; vested in the Alien Property Custodian Application June20, 1939, Serial No. 280,094

Germany June 27, 1938 2 Claims.

In the art of television all mechanic means for scanning a film scan anarea the geometric form of which does not coincide with that of the filmimage.

If, in the simplest case, a scanning drum is used the image of itscylindric surface projected by a lens on the plane of the film is alsocylindric and therefore not sharp on its entire extenslon. The samefault arises in the case of a mirror drum and of other similar meansused for scanning. It makes, of course, no difference .whether theapertures of the scanner are lighted and projected on the film or viceversa.

Another case is that of a Nipkow disc. The scanned area is a trapeziumand the scanned lines are arcs. This "keystone distortion isparticularly noxious for interlaced scanning, as well known.

It is the object of the invention to avoid the described optic faults ina simple manner by imparting to the film, when passing the nlm gate, aslightly crooked cross-section.

The invention is illustrated in mg drawing in which Fig. 1 is a sideview of the general arrangement of the film gate and the guidingrollers,

Fig. 2 shows the said rollers,

Fig. 3 is a cross-section through a scanning arrangement using anapertured drum,

Fig. 4 shows the application of the ,invention in the case of a Nipkowdisc, and

Figs. 5-9 serve for explaining the eifect of this arrangement.

In Fig. 1 l is the film which is conducted by the rollers 2, 5-6, l5-l6and 4 through the film gate 3. As shown by Fig. 2, the rollers 5- 6, andalso the rollers l5-l6, are so shaped as to impart to the film aslightly crooked cross-section, and the form of the film gate 3 (seeFig. 3)

the accompanyis also adapted to keep the film in the same crookedcondition.

' Fig. 3 shows the effect of the described measure in the case of ascanning drum 1 having apertures I! which may be lighted by a lightsource 9. The surface of th drum is projected by a .lens 8 on the filmgate 3. The projected image is, as well known, also cylindrically curvedat a radius which depends on the scale of the projection. According tothe invention the film I is crooked at a radius equal to that of theproiected image so that the optic failure is avoided.

When the scanning is perfected by means of a Nipkow disc I!) (Fig. 4)thefilm gate 3, according to the invention, has to be arranged inclinedat an angle a to the optical axis H-H and the projecting lens 8 at anangle 5 which is practically equal to 11/2. The film I is crooked asdescribed above. The efiect of this arrangement will be described onhand of Figs. 5 to 9.

Fig. 5 shows a fiat film I (cross-section Fig. 6) carrying rectangularimages. It now the same film is crooked (Fig. 9) and inclined at anangle on (Fig. 7) and observed in the direction of the arrow l2, itlooksas shown by Fig, 8. The horizontal edges l3 of the images appearnow curved. By properly choosing the crookedness of the film and theangle a it is easily to obtain that the curvature of the lines I3 isequal to the curvature of the scanning track of an aperture ll projectedon the film. At th same time, by the inclination a of the film, thekeystone effect is completely compensated.

It the scanning drum or disc is provided, instead with simple apertures,with lenses, the proportions described above have to be adapted in anobvious manner.

I claim:

1. A film scanning device comprising a film gate, a scanning disc havinga spiral of apertures, a light source for illuminating said aperturesand a lens system for projecting subsequently the light penetrating saidapertures upon said film gate, said film gate being adapted for keepingthe passing. part oi the film slightly crooked across its lengthandbeing inclined to said film gate, the angle of said inclination being sochosen as to compensate the errors of reproduction caused by thecurvature of said disc and by the keystone distortion.

2. A film scanning device comprising a film gate, a scanning disc havinga spiral of apertures, each being closed by a small lens, a light sourcefor illuminating said apertures and a lens system for projectingsubsequently the light penetrating said apertures upon said film gate,said film gate being adapted for keeping the passingpart of the filmslightly crooked across its length and being inclined to said film gate,the angle of said inclination being so chosen as to compensate theerrors of reproduction caused by the curvature of said disc and by thekeystone distortion.

J QHANNES K'U'FFER.

